The present invention relates to a fluid orifice structure and particularly to an orifice structure having a modulating closure means for varying a pressure signal supplied by the orifice.
In fluid control and operating systems, a signal nozzle device, in combination with control closure structures produce a proportional pressure signal device. In such devices, the closure member is moveably mounted in overlying relationship to the nozzle orifice, thereby controlling the amount of fluid flow through the orifice and correspondingly adjusting the pressure drop across the orifice. By varying the position of the control means, a variable signal is developed which can be used as a control or operating signal. The closure member may be in the form of a canilevered leaf spring element, a flexible diaphragm or the like. Thermostatic devices and other condition sensitive back pressure sensors, for example, may include a bimetal leaf spring element mounted to variably close an orifice, thereby generating a back pressure upstream of the orifice in accordance with a sensed condition. Other fluid and particularly pneumatic devices include fluid signal comparators, amplifiers, switches and like devices in which a flexible diaphragm is sealed within a housing in overlying relationship to an orifice. The diaphragm separates the unit into the signal input chamber, which may or may not include a bias spring, and an input/output chamber which includes the leakport orifice and at least one other port to establish flow into and from the chamber with the flow controlled by the opening and closing of the orifice. These and similar devices are not only well known, having been used for many years, but are relatively highly developed devices providing high degrees of accuracy and response. Further, signal controlling diaphragm devices are relatively simple and readily commercially mass produced.
However, as is well known, signal instability may occur as the closure member moves into relatively close spacement to the orifice. Thus, when supply pressure is supplied to the orifice, the stream issuing from the orifice is of course controlled by the position of the enclosure member. As the closure member moves into close spacement to the orifice, a vibration of the closure member is often created. The vibration is related to and dependent upon the particular spacing of the closure member with respect to the nozzle as well as the material of the closure member or lid and the like. Thus, at a particular balance position, the air moving through the relatively small gap between the lid and orifice tends to create suction with a corresponding reduction in pressure to the downstream side of the orifice. The result is a pressure buildup on the upstream side of the orifice and the closure member tends to move from the orifice to balance and offset such characteristic. This in turn reverses the pressure conditions and the closure member then tends to move toward the orifice. This of course will be recognized as an unstable state, resulting in vibration of the closure member. The member vibrates at a fundamental vibrating frequency related to the dynamics of the air movement and the physical characteristics of the elements. This latter movement not only creates an unstable pressure signal condition, but may well result in a very distinct audible noise. Methods have been suggested for minimizing the vibrational effect. A conventional method is the weighting of the closure member to dampen vibrations. This however reduces the sensitivity of the closure member to the closing force, such as a temperature condition in a bimetal element. U.S. Pat. No. 3,426,970, which issued Feb. 11, 1969, discloses a flat ended nozzle structure with a special encircling structure for developing an air cushion between the lid and a spaced surface exterior to the nozzle which tends to dampen the vibrational characteristics of the flapper or closure member. Such structure would be restricted to a system wherein the air supply is coupled to the orifice such that an emitting jet is created which also interacts with the interrelated surrounding physical structure to develop the desired air cushion.
There is therefore a need for a generally universal means and structure to eliminate such vibrational characteristic and noise in a fluid signal orifice unit, which must of course be adapted to practical commercial implementation.